This application is related to Japanese Patent Application No. 2001-148587 filed on May 18, 2001 whose priority is claimed under 35 USC xc2xa7 119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a transfer film and a process for producing an organic electroluminescent device using the same.
2. Description of the Prior Arts
Recently, there is more need for a flat panel display as a thin and light-weight display device with reduced power consumption, compared to a cathode-ray tube (CRT).
Known as the flat panel display device are a non-luminous liquid crystal display (LCD), a self-luminous plasma display panel (PDP), an electroluminescent (EL; referred to as EL hereafter) display or the like.
Among these displays, the EL display is classified into two types, i.e., an inorganic EL display and an organic EL display, from the viewpoint of a difference in its luminous mechanism and component materials. Particularly, attention has been greatly paid on the organic EL display since it has characteristics of being self-luminous, achieving reduced power consumption, having various luminous colors or the like.
An organic EL device used for the organic EL display has a structure such that an organic light-emitting layer and, according to need, a hole injecting/transporting layer and an electron injecting/transporting layer are sandwiched between a pair of electrodes, at least one of which is transparent. Research has widely been carried out on the EL device since it can be driven at low voltage as well as can luminesce with high luminance.
When a matrix display or color display is to be manufactured in the manufacturing process as described above of the organic EL element used for the organic EL display, a light-emitting layer or cathode is required to be formed into a predetermined pattern. However, an organic material composing the organic EL device is susceptible to damages such as a corrosion or degradation in characteristic due to organic solvent, water, oxygen or the like. Therefore, it is generally difficult to form a pattern by a general photolithography method once a layer containing an organic material is formed.
Methods for performing a pattern formation of light-emitting layers, each of which has a different luminous color, or a cathode include a mask vapor-deposition method for performing a pattern formation by a mask vapor-deposition, a method in which a partitioning wall is formed in advance for performing a pattern formation by a vapor-deposition, an inkjet method for performing a pattern formation by using an ink jet process or the like. These methods are disclosed in, for example, Japanese Unexamined Patent Application Nos. HEI11-135257, HEI8-315981, HEI8-227276 and HEI5-275172. However, the method for forming a pattern formation by the vapor-deposition is not considered to be satisfactory from the viewpoint of production because of the following reasons such that it is difficult to achieve a high precision of the pattern, it is difficult to perform an alignment of a mask with a throwing power considered or the process becomes complicated. Further, the mask vapor-deposition method has a problem that it is difficult to vapor-deposit onto a large-sized substrate, while the ink jet method has a problem of declining productivity since it takes much time to perform the pattern formation by using a large-sized substrate.
On the other hand, a pattern formation method using a transfer method has been known as a method taking the place of the above-mentioned pattern formation. The pattern formation method using the transfer method utilizes a thermal supply by light obtained by laser irradiation or a localized heating element, and is disclosed in Japanese Unexamined Patent Application Nos. HEI9-167684, HEI10-208881, HEI11-237504, HEI11-260549, 2000-12216 and 2000-77182. The pattern formation method using the transfer method can use a large-sized substrate, whereby attention has been paid on this method as a patterned method capable of remarkably shortening a working time.
FIG. 4 shows a sectional view for explaining a conventional pattern formation method using a transfer method with a laser irradiation.
FIG. 4 represents a conventional transfer film and a portion of a process for producing an organic EL device using the same. In this process, a light-to-heat conversion layer 42 and a thermal transmission layer 43 are formed on a film 41, followed by the formation of a cathode layer 44. Subsequently, a light-emitting layer 45b is laminated thereon, and then, a hole injecting/transporting layer 45c is laminated. Thereafter, the film-formed side of the film 41 is attached to a substrate 47 on which a stripe-patterned ITO anode 48 is formed. Then, YAG laser 51 of 13W is selectively irradiated from the backside of the film 41 for forming a cathode shape, whereby a multi-layer 46 is transferred onto the substrate 47. Thereafter, the film 41 is removed, and then, the substrate 47 on which the multi-layer 46 is transferred is connected to a driving means for performing a sealing process, to thereby obtain an organic EL display.
This pattern formation method using the transfer method with a laser irradiation is a dry-type method, so that the organic material composing the organic EL device does not suffer damages from organic solvent or water, as well as that a high-precise pattern can be formed.
However, the aforesaid conventional technique has following problems.
In the case of transferring the multi-layer in the conventional pattern formation method using the transfer method, a satisfactory transfer cannot sometimes be executed due to a difference in melting point of each layer or a laminating order. Further, even when the satisfactory transfer can be obtained, the transfer layer suffers damages from heat if the temperature greatly rises upon transferring, thereby entailing a problem of deteriorating the transfer layer.
The present invention is accomplished for solving the above-mentioned problems, and aims to solve the above-mentioned problems relating to a transfer film and a process for producing an organic EL device using the same and to provide a transfer film and a process for producing an organic EL device using the same.
The present invention provides a transfer film comprising a base film, a transfer layer, and a transfer auxiliary layer formed between the base film and the transfer layer so as to be in contact with at least the transfer layer, this transfer auxiliary layer having a melting point or a glass transition temperature lower than that of the transfer layer, wherein at least a portion of the transfer layer can be thermally transferred onto a substrate.
Further, the present invention provides a process for producing an organic EL device comprising the step of attaching to a substrate a transfer film comprising a base film, a transfer layer to be a constituent layer of the organic EL device and a transfer auxiliary layer formed between the base film and the transfer layer so as to be in contact with at least the transfer layer, this transfer auxiliary layer having a melting point or a glass transition temperature lower than that of the transfer layer, in such a manner that the transfer layer is in contact with a face of the substrate on which the transfer layer is to be transferred: and the step of heating the transfer auxiliary layer from the base film side for transferring at least a portion of the transfer layer onto the substrate, to thereby form the constituent layer of the organic EL device.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit of and scope of the invention will become apparent to those skilled in the art from this detailed description.